The present invention pertains to methods and pharmaceutical compositions for using the selegiline metabolite R(xe2x88x92)desmethylselegiline (also referred to simply as xe2x80x9cdesmethylselegilinexe2x80x9d or xe2x80x9cR(xe2x88x92)DMSxe2x80x9d) either alone or in combination with its enantiomer, entdesmethylselegiline (also referred to as xe2x80x9cS(+)desmethylselegilinexe2x80x9d or xe2x80x9cS(+)DMSxe2x80x9d). In particular, the present invention provides compositions and methods for using these agents in the treatment of selegiline-responsive diseases and conditions, particularly diseases or conditions involving neuronal degeneration or neuronal rescue).
Two distinct monoamine oxidase enzymes are known in the art: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). The cDNAs encoding these enzymes show different promoter regions and distinct exon portions, indicating they are encoded independently at different gene positions. In addition, analysis of the two proteins has shown differences in their respective amino acid sequences.
The first compound found to selectively inhibit MAO-B was R-(xe2x88x92)-N-methyl-N-(prop-2-ynyl)-2-aminophenylpropane, also known as L-(xe2x88x92)-deprenyl, R-(xe2x88x92)-deprenyl, or selegiline. Selegiline has the following structural formula: 
Selegiline is the active ingredient of a human drug product and is known in the art as a component of a therapeutic package. In particular, see Physicians Desk Reference (1995) pp. 2430-2432 (1995 PDR), describing Eldepryl(copyright) Tablets, manufactured by Somerset Pharmaceutical, Inc. and marketed by Sandoz, the active ingredient of which is selegiline. For example, the 1995 PDR describes a 5 mg. selegiline hydrochloride tablet and further describes the manner in which selegiline-containing therapeutic packages are supplied for commercial use or sale. In particular, the 1995 PDR discloses that 5.0 mg Eldepryl Tablets are sold in xe2x80x9cNDC 39506-011-25 bottles of 60 tablets.xe2x80x9d
In commercial use, selegiline-containing therapeutic packages are labeled and otherwise indicated for use in Parkinsonian patients receiving levodopa/carbidopa therapy. The 1995 PDR cited above provides an example of the complete approved labeling that is employed in known therapeutic packages. Accordingly, known in the prior art are therapeutic packages providing one or more unit doses of selegiline as an active ingredient thereof, supplied in a finished pharmaceutical container that contains said unit doses, and further contains or comprises labeling directing the use of said package in the treatment of a human disease or condition as described above.
The selectivity of selegiline in the inhibition of MAO-B is important to its safety profile following oral administration. Inhibition of MAO-A may cause toxic side effects by interfering with the metabolism of tyramine. Tyramine is normally metabolized in the gastrointestinal tract by MAO-A but when MAO-A is inhibited, tyramine absorption is increased following consumption of tyramine-containing foods such as cheese, beer, herring, etc. This results in the release of catecholamines which can precipitate a hypertensive crisis, producing the xe2x80x9ccheese effect.xe2x80x9d This effect is characterized by Goodman and Gilman as the most serious toxic effect associated with MAO-A inhibitors.
One of the metabolites of selegiline is its N-desmethyl analog. Structurally, the desmethylselegiline metabolite is the R(xe2x88x92) enantiomeric form of a secondary amine of the formula: 
Heretofore, desmethylselegiline was not known to have pharmaceutically useful MAO-related effects, i.e., potent and selective inhibitory effects on MAO-B. In the course of determining the usefulness of desmethylselegiline for the purposes of the present invention, the MAO-related effects of desmethylselegiline were more completely characterized. This characterization has established that desmethylselegiline has exceedingly weak MAO-B inhibitory effects and no advantages in selectivity with respect to MAO-B compared to selegiline.
For example, the present characterization established that selegiline has an IC50 value against MAO-B in human platelets of 5xc3x9710xe2x88x929 M whereas R(xe2x88x92)desmethylselegiline""s IC50 value is 4xc3x9710xe2x88x927 M, indicating the latter is approximately 80 times less potent as an MAO-B inhibitor than the former. Similar characteristics can be seen in the following data measuring inhibition of MAO-B and MAO-A in rat cortex mitochondrial-rich fractions:
As is apparent from the above table, selegiline is approximately 128 times more potent as an inhibitor of MAO-B relative to MAO-A, whereas desmethylselegiline is about 97 times more potent as an inhibitor of MAO-B relative to MAO-A. Accordingly, desmethylselegiline appears to have an approximately equal selectivity for MAO-B compared to MAO-A as selegiline, albeit with a substantially reduced potency.
Analogous results are obtained in rat brain tissue. Selegiline exhibits an IC50 for MAO-B of 0.11xc3x9710xe2x88x927 M whereas desmethylselegiline""s IC50 value is 7.3xc3x9710xe2x88x927 M, indicating desmethylselegiline is approximately 70 times less potent as an MAO-B inhibitor than selegiline. Both compounds exhibit low potency in inhibiting MAO-A in rat brain tissue, 0.18xc3x9710xe2x88x925 for selegiline, 7.0xc3x9710xe2x88x925 for desmethylselegiline. Thus, in vitro R(xe2x88x92)desmethylselegiline is approximately 39 times less potent than selegiline in inhibiting MAO-A.
Based on its pharmacological profile as set forth above, R(xe2x88x92)desmethylselegiline as an MAO-B inhibitor provides no advantages in either potency or selectivity compared to selegiline. To the contrary, the above in vitro data suggest that use of desmethylselegiline as an MAO-B inhibitor requires on the order of 70 times the amount of selegiline.
The potency of R(xe2x88x92)desmethylselegiline as an MAO-B inhibitor in vivo has been reported by Heinonen, E. H., et al. (xe2x80x9cDesmethylselegiline, a metabolite of selegiline, is an irreversible inhibitor of MAO-B in human subjects,xe2x80x9d referenced in Academic Dissertation xe2x80x9cSelegiline in the Treatment of Parkinson""s Disease,xe2x80x9d from Research Reports from the Department of Neurology, University of Turku, Turku, Finland, No. 33 (1995), pp. 59-61). According to Heinonen, desmethylselegiline in vivo has only about one-fifth the MAO-B inhibitory effect as selegiline, i.e., a dose of 10 mg of desmethylselegiline would be required for the same MAO-B effect as 1.8 mg of selegiline. In rats, Barbe reported R(xe2x88x92)desmethylselegiline to be an irreversible inhibitor of MAO-B, with a potency about 60 fold lower than selegiline in vitro and about 3 fold lower ex vivo (Barbe, H. O., J. Neural Trans. (Suppl.):32:131 (1990)).
The various diseases and conditions for which selegiline is discloased as being useful include: depression (U.S. Pat. No. 4,861,800); Alzheimer""s disease and Parkinson""s disease, particularly through the use of transdermal dosage forms, including ointments, creams and patches; macular degeneration (U.S. Pat. No. 5,242,950); age-dependent degeneracies, including renal function and cognitive function as evidenced by spatial learning ability (U.S. Pat. No. 5,151,449); pituitary-dependent Cushing""s disease in humans and nonhumans (U.S. Pat. No. 5,192,808); immune system dysfunction in both humans (U.S. Pat. No. 5,387,615) and animals (U.S. Pat. No. 5,276,057); age-dependent weight loss in mammals (U.S. Pat. No. 5,225,446); and schizophrenia (U.S. Pat. No. 5,151,419). PCT Published Application WO 92/17169. discloses the use of selegiline in the treatment of neuromuscular and neurodegenerative disease and in the treatment of CNS injury due to hypoxia, hypoglycemia, ischemic stroke or trauma. In addition, the biochemical effects of selegiline on neuronal cells have been extensively studied. For example, see Tatton, et al., xe2x80x9cSelegiline Can Mediate Neuronal Rescue Rather than Neuronal Protection,xe2x80x9d Movement Disorders 8 (Supp. 1):S20-S30 (1993); Tatton, et al., xe2x80x9cRescue of Dying Neurons,xe2x80x9d J. Neurosci. Res. 30:666-672 (1991); and Tatton, et al., xe2x80x9c(xe2x88x92)-Deprenyl Prevents Mitochondrial Depolarization and Reduces Cell Death in Trophically-Deprived Cells,xe2x80x9d 11th Int""l Symp. on Parkinson""s Disease, Rome, Italy, Mar. 26-30, 1994.
Although selegiline is reported as being effective in treating the foregoing conditions, neither the precise number or nature of its mechanism or mechanisms of action are known.
However, there is evidence that selegiline provides neuroprotection or neuronal rescue, possibly by reducing oxidative neuronal damage, increasing the amount of the enzyme superoxide dismutase, and/or reducing dopamine catabolism. For example, PCT Published Application WO 92/17169 reports that selegiline acts by directly maintaining, preventing loss of, and/or assisting in, the nerve function of animals.
Selegiline is known to be useful when administered to a subject through a wide variety of routes of administration and dosage forms. For example U.S. Pat. No. 4,812,481 (Degussa AG) discloses the use of concomitant selegiline-amantadine in oral, peroral, enteral, pulmonary, rectal, nasal, vaginal, lingual, intravenous, intraarterial, intracardial, intramuscular, intraperitoneal, intracutaneous, and subcutaneous formulations. U.S. Pat. No. 5,192,550 (Alza Corporation) describes a dosage form comprising an outer wall impermeable to selegiline but permeable to external fluids. This dosage form may have applicability for the oral, sublingual or buccal administration of selegiline. Similarly, U.S. Pat. No. 5,387,615 discloses a variety of selegiline compositions, including tablets, pills, capsules, powders, aerosols, suppositories, skin patches, parenterals, and oral liquids, including oil-aqueous suspensions, solutions, and emulsions. Also disclosed are selegiline-containing sustained release (long acting) formulations and devices.
Although a highly potent and selective MAO-B inhibitor, selegiline""s practical use is circumscribed by its dose-dependent specificity for MAO-B, and the pharmacology of selegiline metabolites generated after administration.
The present invention is based upon the surprising discovery that both desmethyl-selegiline (xe2x80x9cDMSxe2x80x9d or xe2x80x9cR(xe2x88x92)DMSxe2x80x9d) and its enantiomer (ent-desmethylselegiline, abbreviated as xe2x80x9cent-DMSxe2x80x9d or xe2x80x9cS(+)DMSxe2x80x9d) are useful in providing selegiline-like effects in subjects, notwithstanding dramatically reduced MAO-B inhibitory activity and an apparent lack of enhanced selectivity for MAO-B compared to selegiline. It has been discovered that desmethylselegiline, ent-desmethylselegiline and their isomeric mixtures provide a more advantageous way of obtaining selegiline-like therapeutic effects in selegiline-responsive diseases or conditions. This is particularly true for diseases or conditions characterized by neuronal degeneration, neuronal trauma or which are hypodopaminergic in nature, i.e. diseases or conditions characterized by reduced dopamine release and formation.
Thus, the present invention provides novel pharmaceutical compositions in which desmethylselegiline, either alone or in a racemic mixture with ent-desmethylselegiline, is employed as the active ingredient and novel therapeutic methods involving the administration of desmethylselegiline. Specifically, the present invention provides:
(1) An improved method for obtaining selegiline-like therapeutic effects in a subject suffering from a selegiline-responsive disease or condition, which comprises: administering to said subject desmethylselegiline in a dosage regime effective to produce said selegiline-like therapeutic effect.
(2) A non-oral pharmaceutical composition comprising an amount of desmethyl-selegiline such that one or more unit doses of said composition administered on a periodic basis is effective to treat one or more selegiline-responsive diseases or conditions in a subject to whom said unit dose or unit doses are administered.
The pharmaceutical composition may contain desmethylselegiline in a substantially enantiomerically pure state or, alternatively, the composition may contain a racemic mixture of enantiomers that are together present in an amount sufficient for one or more unit doses of the composition to be effective in treating a selegiline-responsive disease or condition. The composition may be designed in such a way as to make it suitable for sublingual, buccal, parenteral or transdermal administration and may be adapted for effecting neuronal rescue or protection. The composition may also be adapted for restoring or improving immune system function in a human.
In addition, the present invention is directed to a therapeutic package for dispensing to, or for use in dispensing to, a patient being treated for a neuronal-protective or neuronal-regenerative selegeline-responsive disease or condition. The package contains one or more unit doses, each such unit dose comprising an amount of desmethylselegiline such that periodic administration is effective in treating the patient""s selegeline-responsive disease or condition. The therapeutic package also comprises a finished pharmaceutical container containing the unit doses of desmethylselegiline and further containing or comprising labeling directing the use of the package in the treatment of the selegiline-responsive disease or condition. The unit doses may be adapted for oral administration, e.g. as tablets or capsules, or may be adapted for non-oral administration.
The invention is also directed to a method of dispensing desmethylselegiline to a patient being treated for a neuronal-protective or neuronal-regenerative selegeline-responsive disease or condition. The method comprises providing patients with a therapeutic package having one or more unit doses of desmethylselegiline in an amount such that periodic administration to the patient is effective in treating their selegeline-responsive disease or condition. The package also comprises a finished pharmaceutical container containing the desmethylselegiline and having labeling directing the use of the package in the treatment the selegeline-responsive disease or condition. The unit doses in the package may be adapted for either oral or non-oral administration.
As used herein the term xe2x80x9cselegiline-responsive disease or conditionxe2x80x9d refers to any of the various diseases or conditions in mammals, including humans, for which selegiline is disclosed in the prior art as being useful. In particular, a xe2x80x9cselegiline-responsive disease or conditionxe2x80x9d refers to the various diseases and conditions described above, e.g., Alzheimer""s disease, cognitive dysfunction, neuronal rescue, and the like. The term also refers to the use of selegiline as an appetite suppressant. Similarly, the term xe2x80x9cselegiline-like therapeutic effectxe2x80x9d refers to one or more of the salutary effects reported as being exerted by selegiline in subjects being treated for a selegiline-responsive disease or condition.
The selegiline-responsive diseases or conditions related to neuronal degeneration or trauma which respond to the present methods include Parkinson""s disease, Alzheimer""s disease, depression, glaucoma, macular degeneration, ischemia, diabetic neuropathy, attention deficit disorder, post polio syndrome, multiple sclerosis, impotence, narcolepsy, chronic fatigue syndrome, alopecia, senile dementia, hypoxia, cognitive dysfunction, negative symptomatology of schizophrenia, amyotrophic lateral sclerosis, Tourette""s syndrome, tardive dyskinesia, and toxic neurodegeneration.
The present invention also encompasses the restoration or improvement of immune system function by R(xe2x88x92)DMS or mixtures of R(xe2x88x92)DMS and S(+)DMS. Such improvement or restoration has been reported to occur when selegiline is administered to animals. The conditions or diseases treatable include age-dependent immune system dysfunction, AIDS, infectious diseases and immunological loss due to cancer chemotherapy.
Desmethylselegiline may be administered either by a route involving gastrointestinal absorption or by a route that does not rely upon gastrointestinal absorption. Depending upon the particular route employed, desmethylselegiline is administered in the form of the free base or as a physiologically acceptable non-toxic acid addition salt. Such salts include those derived from organic and inorganic acids such as, without limitation, hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid, methanesulphonic acid, acetic acid, tartaric acid, lactic acid, succinic acid, citric acid, malic acid, maleic acid, sorbic acid, aconitic acid, salicylic acid, phthalic acid, embonic acid, enanthic acid, and the like. The use of salts, especially the hydrochloride, is particularly desirable when the route of administration employs aqueous solutions, as for example parenteral administration; use of delivered desmethylselegiline in the form of the free base is especially useful for transdermal administration. Accordingly, reference herein to the administration of DMS or ent-DMS or to mixtures thereof encompasses both the free base and acid addition salt forms.
The optimal daily dose of desmethylselegiline, or of a combination of R(xe2x88x92)DMS and S(+)DMS, useful for the purposes of the present invention is determined by methods known in the art, e.g., based on the severity of the disease or condition being treated, the condition of the subject to whom treatment is being given, the desired degree of therapeutic response, and the concomitant therapies being administered to the patient or animal. Ordinarily, however, the attending physician or veterinarian will administer an initial dose of at least about 0.015 mg/kg, calculated on the basis of the free secondary amine, with progressively higher doses being employed depending upon the route of administration and the subsequent response to the therapy. Typically the daily dose will be about 0.5 mg/kg and may extend to about 1.0 mg/kg of the patient""s body weight depending on the route of administration. Again, all such doses should be calculated on the basis of the free secondary amine. These guidelines further require that the actual dose be carefully titrated by the attending physician or veterinarian depending on the age, weight, clinical condition, and observed response of the individual patient or animal.
The daily dose can be administered in a single or multiple dosage regimen. Either oral or non-oral dosage forms may be used and may permit, for example, a continuous release of relatively small amounts of the active ingredient from a single dosage unit, such as a transdermal patch, over the course of one or more days. This is particularly desirable in the treatment of chronic conditions such as Parkinson""s disease, Alzheimer""s disease, and depression. Alternatively, it can be desirable in conditions such as ischemia or neural damage to administer one or more discrete doses by a more direct systemic route such as intravenously or by inhalation. In still other instances such as glaucoma and macular degeneration, localized administration, such as via the intraocular route, can be indicated.
Pharmaceutical compositions containing desmethylselegiline and/or ent-desmethylselegiline can be prepared according to conventional techniques. For example, preparations for parenteral routes of administration for desmethylselegiline, e.g., intramuscular, intravenous and intraarterial routes, can employ sterile isotonic saline solutions. Sterile buffered solutions can also be employed for intraocular administration.
Transdermal dosage unit forms of desmethylselegiline and/or ent-desmethylselegiline can be prepared utilizing a variety of previously described techniques (see e.g., U.S. Pat. Nos. 4,861,800; 4,868,218; 5,128,145; 5,190,763; and 5,242,950; and EP-A 404807, EP-A 509761, and EP-A 593807). For example, a monolithic patch structure can be utilized in which desmethylselegiline is directly incorporated into the adhesive and this mixture is cast onto a backing sheet.
Alternatively desmethylselegiline, and/or ent-desmethylselegiline, can be incorporated as an acid addition salt into a multilayer patch which effects a conversion of the salt to the free base, as described for example in EP-A 593807.
Desmethylselegiline and/or ent-desmethylselegiline can also be administered by a device employing a lyotropic liquid crystalline composition in which, for example, 5 to 15% of desmethylselegiline is combined with a mixture of liquid and solid polyethylene glycols, a polymer, and a nonionic surfactant, optionally with the addition of propylene glycol and an emulsifying agent. For further details on the preparation of such transdermal preparations, reference can be made to EP-A 5509761.
Since the term xe2x80x9cent-desmethylselegilinexe2x80x9d refers to the S(+) isomeric form of desmethylselegiline, reference above to mixtures of desmethylselegiline and ent-desmethylselegiline includes both racemic and non-racemic mixtures of optical isomers.
Subjects treatable by the present preparations and methods include both human and non-human subjects for which selegiline-like therapeutic effects are known to be useful. Accordingly, the compositions and methods above provide especially useful therapies for mammals, especially domesticated mammals. Thus, the present methods and compositions are used in treating selegiline-responsive diseases or conditions in canine and feline species.
Successful use of the compositions and methods above requires employment of an effective amount of desmethylselegiline, or mixtures of desmethylselegiline and ent-desmethylselegiline. Although both desmethylselegiline and ent-desmethylselegiline are dramatically less potent than selegiline as inhibitors of MAO, employment of these agents, or a mixture of these agents, for neuroprotection does not require a commensurately increased dosage to obtain a selegiline-like therapeutic response. Surprisingly, dosages necessary to attain a selegiline-like therapeutic appear to be on the same order as the known doses of selegiline. Accordingly, because both desmethylselegiline and ent-desmethylselegiline exhibit a much lower inhibition of MAO-A at such dosages, desmethylselegiline and ent-desmethylselegiline provide a substantially wider margin of safety with respect to MAO-A associated toxicity compared to selegiline. In particular, the risk of the adverse effects of MAO-A inhibition, e.g., hypertensive crisis, are minimized due to the 40-70 fold reduced potency for MAO-A inhibition.
As described above and notwithstanding its demonstrably inferior inhibitory properties with respect to MAO-B inhibition, desmethylselegiline and its enantiomer appear to be at least as effective as selegiline in treating certain selegiline-responsive conditions, e.g., conditions resulting from neuronal degeneration or neuronal trauma. Although the oral route of administration will generally be most convenient, drug may be administered by the parenteral, topical, transdermal, intraocular, buccal, sublingual, intranasal, inhalation, vaginal, rectal or other routes as well.
As noted above, the present invention encompasses the additional discovery that desmethylselegiline can be employed either alone or in mixture with desmethylselegiline. Desmethylselegiline, its enantiomer and mixtures thereof are conveniently prepared by methods known in the art, as described in Example 1.